Can I make a shortlink site using Netlify's redirecting service?
Yes.
Can I make it dynamically generate from a directory of files, thus ensuring uniqueness and easy additions?
Also yes.
The Makefile's default target is site/_redirects. That file has a pretty simple format so I'm going to dynamically generate it with a relatively simple Node script.
To add more link targets, add a file to the links directory. The name of the file becomes the shortlink suffix and the contents become the URL that we 301 redirect to.